[Libvir] [for discussion only] virDomainBlockPeek preliminary implementation

[Richard W.M. Jones]

The attached patch (for discussion only) adds a virDomainBlockPeek call, 
allowing callers to peek into the block devices of domains.

+/**
+ * virDomainBlockPeek:
+ * @dom: pointer to the domain object
+ * @path: path to the block device
+ * @offset: offset within block device
+ * @size: size to read
+ * @buffer: return buffer (must be at least size bytes)
+ *
+ * This function allows you to read the contents of a domain's
+ * disk device.
+ *
+ * Typical uses for this are to determine if the domain has
+ * written a Master Boot Record (indicating that the domain
+ * has completed installation), or to try to work out the state
+ * of the domain's filesystems.
+ *
+ * (Note that in the local case you might try to open the
+ * block device or file directly, but that won't work in the
+ * remote case, nor if you don't have sufficient permission.
+ * Hence the need for this call).
+ *
+ * 'path' must be a device or file corresponding to the domain.
+ * In other words it must be the precise string returned in
+ * a <disk><source dev='...'/></disk> from
+ * virDomainGetXMLDesc.
+ *
+ * 'offset' and 'size' represent an area which must lie entirely
+ * within the device or file.  'size' may be 0 to test if the
+ * call would succeed.
+ *
+ * 'buffer' is the return buffer and must be at least 'size' bytes.
+ *
+ * Returns: 0 in case of success or -1 in case of failure.
+ */
+int
+virDomainBlockPeek (virDomainPtr dom,
+                    const char *path,
+                    long long offset /* really 64 bits */,
+                    size_t size,
+                    void *buffer)

The patch doesn't include:
  - remote
  - qemu
  - Xen < 3.0.3 inactive domains

I will add these if I get favourable feedback.

Rich.

-- 
Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/
Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod
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